Publisher Summary This chapter discusses the role of glutathione (GSH) and glutathione s-transferases in metabolism of chemical carcinogens and other electrophilic agents. GSH is a tripeptide (I) that is present in nearly all living cells and is the most abundant sulfhydryl compound present in animal tissues, mainly in the cytosol. The chapter illustrates the wide range of electrophilic agents, including several known mutagens and carcinogens, which conjugate with GSH, a process usually catalyzed by the GSH S-transferases. This conjugation is probably a protective mechanism and is the initial stage in mercapturic acid biosynthesis for the elimination of foreign compounds from the body. GSH S-transferases provide protection not only by catalyzing the conjugation of a potential toxicant with GSH, but also by preferentially binding, even covalently, that toxicant. The reactive electrophiles that conjugate with GSH also bind to DNA, RNA, and protein and identification of GSH conjugates provide information on the nature of these biologically active intermediates or even their immediate precursors. Thus, the knowledge of the way in which mutagens and carcinogens are metabolized is essential to a better understanding of their mode of action and of the processes for their detoxication.

The role of glutathione and glutathione S-transferases in the metabolism of chemical carcinogens and other electrophilic agents.

The aim of this study was to screen various solvent extracts of whole plant of Torilis leptophylla to display potent antioxidant activity in vitro and in vivo, total phenolic and flavonoid contents in order to find possible sources for future novel antioxidants in food and pharmaceutical formulations. A detailed study was performed on the antioxidant activity of the methanol extract of whole plant of Torilis leptophylla (TLM) and its derived fractions {n-hexane (TLH), chloroform (TLC) ethyl acetate (TLE) n-butanol (TLB) and residual aqueous fraction (TLA)} by in vitro chemical analyses and carbon tetrachloride (CCl4) induced hepatic injuries (lipid peroxidation and glutathione contents) in male Sprague-Dawley rat. The total yield, total phenolic (TPC) and total flavonoid contents (TFC) of all the fractions were also determined. TLM was also subjected to preliminary phytochemical screening test for various constituents. The total phenolic contents (TPC) (121.9±3.1 mg GAE/g extract) of TLM while total flavonoid contents (TFC) of TLE (60.9 ±2.2 mg RTE/g extract) were found significantly higher as compared to other solvent fractions. Phytochemical screening of TLM revealed the presence of alkaloids, anthraquinones, cardiac glycosides, coumarins, flavonoids, saponins, phlobatannins, tannins and terpenoids. The EC50 values based on the DPPH (41.0±1 μg/ml), ABTS (10.0±0.9 μg/ml) and phosphomolybdate (10.7±2 μg/ml) for TLB, hydroxyl radicals (8.0±1 μg/ml) for TLC, superoxide radicals (57.0±0.3 μg/ml) for TLM and hydrogen peroxide radicals (68.0±2 μg/ml) for TLE were generally lower showing potential antioxidant properties. A significant but marginal positive correlation was found between TPC and EC50 values for DPPH, hydroxyl, phosphomolybdate and ABTS, whereas another weak and positive correlation was determined between TFC and EC50 values for superoxide anion and hydroxyl radicals. Results of in vivo experiment revealed that administration of CCl4 caused a significant increase in lipid peroxidation (TBARS) while decrease in GSH contents of liver. In contrast, TLM (200 mg/kg bw) and silymarin (50 mg/kg bw) co-treatment effectively prevented these alterations and maintained the antioxidant status. Data from present results revealed that Torilis leptophylla act as an antioxidant agent due to its free radical scavenging and cytoprotective activity.

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Antioxidant activity, total phenolic and total flavonoid contents of whole plant extracts Torilis leptophylla L

Levels of Zn, Cu, Cd, As, and Pb in the kidney, Liver, Gills and Heart of African cat fish (Clarias gariepinus) from the Ogun River in Ogun State located close to six major industries in the South Western part of Nigeria, were determined using Bulk Scientific Atomic Absorption Spectrophotometer. Fishes were also collected from Government owned fish farm in Agodi, Ibadan which was considered a reference site. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), glutathione (GSH) concentration and malondialdehyde (MDA) formation were also determined. The trend of accumulation of the metals in the organs is as follows: Heart - Zn > Cu > Pb > As > Cd; Gills - Zn > Cu > Pb > Cd > As; Kidney - Zn > Cu > Pb > As > Cd; Liver - Zn > Cu > Pb > As > Cd. The order of concentration of the metals in the organs is as follows: Arsenite - Kidney > Liver > Gills > Heart; Zinc - Gills > Liver > Kidney > Heart; Lead- Liver > Kidney > Gills > Heart; Copper- Kidney > Liver > Gills > Heart; Cadmium > Liver > Gills > Kidney > Heart. The levels of heavy metals ranged between 0.25- 8.96 ppm in the heart, 0.69- 19.05 ppm in the kidneys, 2.10-19.75 ppm in the liver and 1.95-20.35 ppm in the gills. SOD activity increased by 61% in the liver, 50% in the kidney and in the heart by 28 % while a significant decrease (44%) was observed in the gill of Clarias gariepinus from Ogun river compared to that Agodi fish farm (P<0.001). On the contrary there was 46%, 41%, 50% and 19% decrease in CAT activity in the liver, kidney, gills and heart respectively. The levels of GST activities in the liver, kidney and heart of Clarias gariepinus from Ogun river increased by 62%, 72% and 37% respectively (P<0.001) whereas there was a significant decrease (41%) in the gills (P<0.05) compared to that from the Agodi fish farm. GSH concentration increased by 81%, 83% and 53% in the liver, kidney and heart respectively but decreased by 44% in the gills. MDA levels of Clarias gariepinus were significantly (P<0.001) elevated in the liver, kidney, gills and heart by 177%, 102%, 168% and 71% respectively compared to that from Agodi fish farm. Overall, the results demonstrate that alteration in the antioxidant enzymes, glutathione system and induction of lipid peroxidation reflects the presence of heavy metals which may cause oxidative stress in the Clarias gariepinus from Ogun River. The study therefore provides a rational use of biomarkers of oxidative stress in biomonitoring of aquatic pollution.

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Biomarkers of oxidative stress and heavy metal levels as indicators of environmental pollution in African cat fish (Clarias gariepinus) from Nigeria Ogun River.

Evaluation of the Cd/hemoglobin affinity assay for the rapid determination of metallothionein in biologival tissues

Biomarkers of oxidative stress: a comparative study of river Yamuna fish Wallago attu (Bl. & Schn.).

This laboratory has previously postulated that bromobenzene-induced hepatic necrosis results from the formation of a reactive metabolite that arylates vital cellular macromolecules. Accordingly, the severity of liver necrosis has been compared with the formation of metabolites of bromobenzene and with covalent binding of metabolites in vivo and in vitro after various pretreatment regimens that alter hepatotoxicity. These data provide direct kinetic evidence that 3,4-bromobenzene oxide is the reactive hepatotoxic metabolite. The studies also demonstrate that the hepatotoxic metabolite is preferentially conjugated (detoxified) with glutathione, thereby depleting glutathione from the liver. Liver necrosis and arylation of cellular macromolecules occur only when glutathione is no longer available. Thus, a dose threshold exists for bromobenzene-induced hepatic necrosis.

N Zampaglione

Papers

Bromobenzene-Induced Liver Necrosis. Protective Role of Glutathione and Evidence for 3,4-Bromobenzene Oxide as the Hepatotoxic Metabolite